All organisms are constantly exposed to stressful conditions as a consequence of normal cell growth and division, infection, exposure to pharmacological agents, environmental insults or unregulated cell growth in the cancerous state. Heat Shock Factors (HSF) are a class of highly conserved transcription factors which sense and respond to a wide variety of cellular stresses to regulate the expression of genes that are vital to survival during stress and for the establishment of normal cellular homeostatic controls. HSF regulates the expression of genes encoding protein chaperones, which play pivotal roles in protein folding, maturation, targeting and the activation of key cellular growth control proteins, as well as genes encoding proto-oncoproteins, pain receptors, cytokines and immune surveillance molecules. In this application we describe experiments with the overall objective of understanding how HSF proteins sense distinct stresses to activate gene expression, using both yeast and human cells as model systems. First, the mechanisms by which yeast cells sense growth control signals through glucose, and transmit this information to activate HSF function, will be explored through genetic, biochemical and molecular biology approaches. Secondly, using both yeast cells and human cells, as well as in vitro techniques, the mechanisms whereby cells retain human HSF proteins in an inactive form, and respond to stress signals to activate HSF molecules, will be investigated. Third, the molecular mechanisms by which distinct human HSF isoforms activate distinct target genes, and the identification of these genes, will be investigated in both yeast and human cells. The experiments described in this proposal will provide insight into how this highly conserved class of stress- responsive transcription factors sense and respond to stresses that occur during normal growth, and disease states, to maintain cellular regulation.